The present invention relates to a shadow mask type color cathode ray tube, and more particularly to a shadow mask type color cathode ray tube provided with a shadow mask capable of being installed into the color cathode ray tube without causing curvature distortions or reduction in strength of the shadow mask by reducing curls occurring in the skirt portion thereof in press-forming the shadow mask.
Generally in assembling a shadow mask type color cathode ray tube, a skirt portion of the shadow mask formed by press-forming is fitted within a support frame, the shadow mask is affixed to the support frame by spot welding, and then the support frame is suspended within a panel portion of the color cathode ray tube such that the shadow mask is positioned adjacent to, but spaced from a phosphor film formed on the inner surface of a faceplate of the panel portion.
FIGS. 4A to 4C are respectively structural views showing an example of the shadow mask used for a conventional color cathode ray tube. FIG. 4A is a front view of the shadow mask, FIG. 4B is an enlarged fragmentary side view of an area in the vicinity of welds in the skirt portion thereof, and FIG. 4C is a sectional view of a region extending from an imperforate portion to the skirt portion. In FIGS. 4A to 4C, reference numeral 41 designates a shadow mask; 42 is an apertured portion; 43 is an imperforate portion; and 44 is a skirt portion, and x marks indicate welds.
The shadow mask 41 has a curved apertured portion 42 having a multiplicity of electron-transmissive apertures, a curved imperforate portion 43 surrounding and integral with the apertured portion 42 and a skirt portion 44 bent back from a periphery of the curved imperforate portion 43, and is usually integrally formed by press-forming a multi-apertured thin sheet-like metal blank.
In this case, the multi-apertured thin sheet-like metal blank is very thin and relatively weak in strength. Therefore, the press-formed shadow mask 41 is not always good in forming characteristics. Especially, the skirt portion 44 of the shadow mask 41 curls outwardly by a distance S from a straight line passing through a bend line between the imperforate portion 43 and the skirt portion 44 and parallel to the longitudinal axis of the cathode ray tube, in a region centering about the center of each side of the generally rectangular shadow mask 41, as shown in FIG. 4C.
The skirt portion 44 of the press-formed shadow mask 41 is fitted within or outside a support frame (not shown), and is welded and affixed to the support frame at a few points. As indicated in FIG. 4B by x marks, welds of the skirt portion 44 and the support frame are located two in the vicinity of the center of each of the long and short sides of the shadow mask 41, and one at each of the four corners thereof, for example.
When the conventional shadow mask 41 is press-formed, occurrence of the curl S in the skirt portion 44 is unavoidable, and if the curl S is excessively large, it is an obstacle to fitting the skirt portion 44 into the support frame and welding the fitted portion thereof to the support frame, resulting in reduction of workability.
Further, when the skirt portion 44 of the conventional shadow mask 41 having the large curl S is forcibly fitted in the support frame, the stress applied to the skirt portion 44 is transmitted to the imperforate portion 43 and the apertured portion 42, and distorts the curved contour of the apertured portion 42 of the shadow mask 41, and as a result, the color selection property of the shadow mask 41 is degraded, and the strength of the shadow mask 41 is reduced.